Spring drought is becoming a frequently occurring stress factor in temperate forests. However, the understanding of tree resistance and resilience to the spring drought remains insufficient. In this study, European beech (Fagus sylvatica L.) seedlings at the early stage of leaf development were moderately and severely drought stressed for 1 month and then subjected to a 2-week recovery period after rewatering. The study aimed to disentangle the complex relationships between leaf gas exchange, vascular anatomy, tree morphology and patterns of biomass allocation. Stomatal conductance decreased by 80 and 85% upon moderate and severe drought stress, respectively, which brought about a decline in net photosynthesis. However, drought did not affect the indices of slow chlorophyll fluorescence, indicating no permanent damage to the light part of the photosynthetic apparatus. Stem hydraulic conductivity decreased by more than 92% at both drought levels. Consequently, the cambial activity of stressed seedlings declined, which led to lower stem biomass, reduced tree ring width and a lower number of vessels in the current tree ring, these latter also with smaller dimensions. In contrast, the petiole structure was not affected, but at the cost of reduced leaf biomass. Root biomass was reduced only by severe drought. After rewatering, the recovery of gas exchange and regrowth of the current tree ring were observed, all delayed by several days and by lower magnitudes in severely stressed seedlings. The reduced stem hydraulic conductivity inhibited the recovery of gas exchange, but xylem function started to recover by regrowth and refilling of embolized vessels. Despite the damage to conductive xylem, no mortality occurred. These results suggest the low resistance but high resilience of European beech to spring drought. Nevertheless, beech resilience could be weakened if the period between drought events is short, as the recovery of severely stressed seedlings took longer than 14 days.

中文翻译：

---

欧洲山毛榉幼苗在叶片发育期间对干旱胁迫的抗性和韧性。

春季干旱正在成为温带森林中经常发生的压力因素。但是，人们对树木对春季干旱的抵抗力和恢复力的了解仍然不足。在这项研究中，欧洲山毛榉（Fagus sylvaticaL.）将叶片发育初期的幼苗进行中度和严重干旱胁迫1个月，然后在复水后经历2周的恢复期。该研究旨在弄清叶片气体交换，血管解剖结构，树木形态和生物量分配模式之间的复杂关系。在中度和重度干旱胁迫下，气孔导度分别降低了80％和85％，这导致净光合作用下降。然而，干旱并没有影响慢叶绿素荧光指数，表明对光合作用装置的轻部分没有永久性损害。在两个干旱水平下，茎的水力传导率均下降了92％以上。因此，受胁迫的幼苗的冈比亚活性下降，导致茎生物量降低，减少了年轮宽度，并减少了当前年轮中的船只数量，后者的尺寸也较小。相反，叶柄的结构没有受到影响，但是是以减少叶片生物量为代价的。严重干旱只会减少根系生物量。再浇水后，观察到当前树木年轮的气体交换和再生长的恢复，在严重胁迫的幼苗中，所有这些都延迟了几天并且幅度降低了。降低的茎部水力传导率抑制了气体交换的恢复，但是木质部功能开始通过栓塞血管的再生和再填充而恢复。尽管损坏了导电木质部，但没有发生死亡。这些结果表明欧洲山毛榉对春季干旱的抵抗力较低，但弹性较高。不过，